1. Field of the Invention
The present invention relates to an X-ray diffraction device of a wavelength-classifying type, having a function whereby X-rays that include a plurality of X-rays of different wavelengths may be classified into X-rays of each of the wavelengths, and X-ray measurements may be carried out using X-rays of the individual wavelengths.
2. Description of the Related Art
In the field of X-ray diffraction devices, there are instances in which it is desired to use a plurality of characteristic X-rays of different wavelengths when measuring a single substance to be measured. For example, for analysis in situations where the wave vector of the X-rays necessitates large radial range (for example, as in radial distribution analysis), or in the case of the multi-wavelength anomalous dispersion (MAD) method used in analyzing the structures of native proteins, there are instances in which a plurality of X-rays of different wavelengths are desired.
Hitherto, one procedure employed in instances where a plurality of X-rays of different wavelengths are used in an X-ray diffraction device involves swapping out the X-ray tube. The operation to swap out the X-ray tube is typically a manual operation performed by the operator. Because of this, problems have been encountered in regard to the considerable time needed for the swap out, and the difficultly of adjusting the emission optical path of the X-rays subsequent to swap out.
In particular, in the case of a demountable X-ray tube, which is a tube that uses a rotating anti-cathode, namely, a rotor target, as the anti-cathode, namely, as the target, swapping out the demountable X-ray tube requires first releasing the vacuum in the vacuum chamber in which the demountable X-ray tube is disposed, before swapping the tube out; and subsequently carrying out an operation to reestablish a vacuum state. In such instances, an extremely long period of time is needed before the vacuum chamber interior can be restored to a degree of vacuum enabling generation of X-rays.
Also, because demountable X-ray tubes are quite heavy, a risk is presented in regard to the demountable X-ray tube being dropped during the replacement operation, or of the demountable X-ray tube coming into contact with the device chassis. Another risk is that coolant introduced into the interior of the X-ray tube will drip down into the vacuum chamber interior during the swap-out operation of the X-ray tube.
Furthermore, in many instances, once the X-ray tube is replaced, the position of the X-ray generation source will be very slightly shifted out of position for reasons relating to the accuracy of mechanical attachment, and it has therefore been necessary to make readjustments to the optical system for measurement, which is supported by a goniometer inside the X-ray diffraction device.
Because operations to replace X-ray tubes are extremely laborious and time-consuming as discussed above, the operational efficiency of replacing a plurality of X-ray sources in a single X-ray generation device is extremely poor.
On the other hand, in instances of using a plurality X-rays of different wavelengths in an X-ray diffraction device, one method involves preparing an X-ray generation device for each of a plurality of X-ray sources of different wavelengths. However, a single X-ray generation device is quite expensive, making it extremely difficult to provide a plurality of these devices.
Furthermore, in instances where a substance being measured is a substance unable to maintain crystal structure for an extended period, the crystal structure may change during replacement of the X-ray tube or in the course of conducting measurements multiple times, so that sometimes accurate measurement data cannot be obtained.
To address the aforementioned problems, there have been proposed a multitude of X-ray generation devices adapted to generate a plurality of types of X-rays simultaneously, or to periodically switch among generating a plurality of types of X-rays. For example, one known device of this kind is an X-ray generation device that uses a so-called stripe target. With an ordinary rotating anti-cathode (namely, a rotor target), a metal of the same given type is deposited uniformly on a round tubular metal face which constitutes the X-ray generating section. With a stripe target, on the other hand, two or more different types of metal are deposited to predetermined width in cyclically alternating fashion (namely, in a stripe pattern) along the direction in which thermal electrons scan the surface of the target.
When this stripe target is rotated at high speed, X-rays of different wavelengths that correspond to the different types of metal can be elicited in a constant cycle. X-rays having wavelengths used for measurement can then be sorted using an analyzing crystal (namely, a monochromator). In an instance of changing the wavelength, the analyzing crystal is rotated about its own centerline to change the angle with respect to the impinging X-rays, or the analyzing crystal is exchanged for one of a different type.
In a known method according to Japanese Patent Laid Open Publication No. H7-073831, in place of a wavelength classification method that uses an analyzing crystal, diffracted X-ray data are acquired only at times of X-rays from the same given metal, in synchronization with rotation of a stripe target. Another method according to Japanese Patent Laid Open Publication No. H5-152091 teaches classification of X-ray wavelengths by opening and closing of a rotating shutter in synchronization with rotation of a stripe target.
Yet another method according to Japanese Patent Laid Open Publication No. H11-339703 teaches disposing ring shapes, namely, annular shapes, of two or more different metals along a direction perpendicular to the direction in which the thermal electrons scan the surface of the target, and classifying X-ray wavelengths by changing the electron emission angle of the electron gun. Still another method according to Japanese Patent Laid Open Publication No. 2007-323964 teaches disposing ring shapes of two or more different metals along a direction perpendicular to the direction in which the thermal electrons scan the surface of the target, and classifying X-ray wavelengths through parallel travel of the electron gun.
Another method according to Japanese Patent Laid Open Publication No. H5-089809 teaches disposing ring shapes of two or more different metals along a direction perpendicular to the direction in which the thermal electrons scan the surface of the target, and classifying X-ray wavelengths through travel of the target relative to the electron gun. Yet another method according to Japanese Patent Laid Open Publication No. H5-135722 teaches disposing ring shapes of two or more different metals along a direction perpendicular to the direction in which the thermal electrons scan the surface of the target, and classifying X-ray wavelengths by changing the direction of advance of the electron beam to change the metal being struck by the electrons.
In a device according to Japanese Patent Laid Open Publication No. H6-215710, ring shapes of two or more different metals are disposed, electron guns are disposed facing the individual different metals, and X-rays of different wavelengths are generated simultaneously while a plurality of types of measurement are carried out simultaneously using the X-rays. Also, in a known target for generating X-rays of different wavelengths according to Japanese Patent Laid Open Publication No. H5-325851, the target is formed of an alloy which is a combination of different metals.
In a known X-ray generation device according to Japanese Patent Laid Open Publication No. H8-094547, a plurality of X-ray tubes are provided for generating X-rays of different wavelengths, and control means are provided for controlling operation of these X-ray tubes under individually appropriate conditions. In a known X-ray diffraction device according to Japanese Patent Laid Open Publication No. 2002-039970, a plurality of X-ray tubes are provided for generating X-rays of different wavelengths, X-rays are caused to impinge on a sample from different directions, and a plurality of types of diffracted X-rays arising from X-rays of different wavelengths are received by a two-dimensional X-ray detector as they are emitted from the sample.
Further, in a known X-ray diffraction device according to Japanese Patent No. 4074874, X-rays of mutually different wavelengths are elicited respectively from an upper half region and a lower half region of a rotating target, and these bombard a single sample, whereupon diffracted X-rays emitted from an upper half region and diffracted X-rays emitted from a lower half region of the sample are detected simultaneously by a two-dimensional CCD detector. According to this device, measurement data based on X-rays of different wavelengths can be obtained simultaneously through just one measurement.